Question

In a Helium gas discharge tube every second 40 x ${10}^{18}H{e}^{+}$ (ions) move towards the right through a cross - section of the tube, while n electrons move to the left in the same time. If the current in the tube is 8A towards right then n = ?

• A. 10 x ${10}^{18}$
• B. 3 x ${10}^{19}$
• C. 3 x ${10}^{20}$
• D. 3 x ${10}^{21}$

Answer 1

The correct option is A 10 x ${10}^{18}$

Net current$=$current due to $H{e}^{+}+$ current elements

$\Rightarrow 8Amp=\frac{40\times {10}^{18}\times 1.6\times {10}^{-19}}{1\sec }+\frac{n\times 1.6\times {10}^{-19}}{1\sec }$

$\Rightarrow \frac{8}{1.6\times {10}^{-19}}=n+40\times {10}^{18}$

but $n+40\times {10}^{18}=50\times {10}^{18}$

so, $n=10\times {10}^{18}={10}^{19}$.